Fluctuations of monsoon activity

Abstract

In order to study the evolution of flow patterns associated with 'strong' and 'break' monsoon we have studied six cases each of such epochs during the period 1965 to 1973. As we are interested in the departure of the flow patterns from the normal, we have subtracted long term climatological pentad means from the daily data and constructed anomaly wind, height and thickness charts at standard levels.
 The several contrasting features during the epochs as well as prior to the epochs. A few days prior to the beginning of the strong monsoon epoch (usually in association with a depression), an eastwest anomaly trough is seen extending from SE Asia to peninsular India in the lower and, middle tropospheres. The trough over peninsular India shifts northwards with the advance of the epoch. Westward movement of a cyclonic anomaly from across Southeast Asia IS also seen. In the upper troposphere a warm anomaly ridge isseen to the northwest of India.
 Prior to the beginning of breaks, however, an anomaly ridge is seen extending from peninsular India to Malaysia in the lower and middle tropospheres. This feature also shows some northward shift with the advance of the epoch. In the upper troposphere, an anomaly trough is seen to the northwest of India.

Towards a realistic MISO simulation: impact of rectification

“…MISOs are the periodic oscillation of dry (break) and wet (active) spells of precipitation which have a time scale longer than diurnal and synoptic variability but shorter than a season. Earlier studies (ALEXANDER et al 1978;Yasunari 1980; Goswami and Ajaya Mohan 2001) have shown that MISOs have a preferred scale of periodicity between 20 to 90 days. A repeated northward movement of cloud bands from south of the equator to the foothills of the Himalayas is associated with active and break spells of monsoon (Yasunari 1979; Sikka and Gadgil 1980; Krishnamurti and Subrahmanyam 1982).…”

High‐intensity rainfall over northeast India: Spatial pattern, short‐term fluctuations and associated multiscale oscillations

“…Additionally, break monsoon conditions, when the monsoon trough lies close to the foothills of the Himalayas, are extremely conducive for rainfall in NEI (Rahecha & Pisharoty, 1996; Ramamurthy, 1969; Rao, 1976). Several studies have provided extensive documentation of the active and break monsoon conditions in terms of intraseasonal oscillations (ISO) (Alexander et al, 1978; Goswami & Ajayamohan, 2001; Krishnamurthy & Shukla, 2007, 2008; Krishnamurti & Bhalme, 1976).…”

On global summer monsoonal drought mechanics

“…Such years with below-normal rainfall are termed by Asian meteorologists as 'drought years' or 'bad monsoon' years. The anomalies for drought situation over Indian region were studied extensively by a number of workers (Ramamurty 1969;Joseph 1978;Alexander et al 1978). The main observations for drought situation are that (i) the rainfall is well below normal or completely absent over north Indian plains region, (ii) the surface pressure shows a positive anomaly of.…”